Add pkg_version to nginx class interface.  It is used to set the ensure
atribute on Package['Nginx'].  Default value is 'present'.  Only
supports redhat variants right now.
pass $pkg_version to Class['nginx::package']
fix pkg_version so it only applies to nginx and not ancillary packages.
Merge pull request #3 from hubspotdevops/add_pkg_version_parameter

Add pkg version parameter